This invention relates generally to advances in medical systems and procedures for prolonging or improving human life. More particularly, this invention relates to an improved method and system for advancing a probe or an electrode into the human body in finely graded steps while detecting the position of the probe advancement.
In the field of neurosurgical stereotaxy, electrodes and probes of various kinds may be advanced into the brain of a patient. In the case of deep brain stimulation (DBS) or radiofrequency (RF) lesion making, microelectrodes are typically advanced from a stereotactic frame into the brain in very small steps, sometimes of micron incrementation. These microelectrodes typically have tips with lengths of several microns to several hundred microns. In some applications recordings of electrical activity of brain cells deep in the brain are recorded by electrical signal monitoring from the microelectrode as it is incrementally advanced into the brain.
Microdrives for such brain probes may include mechanical sliding devices and mechanical screw devices that are attached to the carrier of the stereotactic frame. These devices typically are cooperatively connected to the probe so that advancement of the probe into the patient""s brain, for example, can be done while visually reading a mechanical scale or digital readout. In some instances, the operation of these devices involves turning a mechanical screw or rack-and-pinion to advance the position of the electrode mechanically.
By reference, the stereotactc frames of Radionics, Inc., Elekta AB, and the TrentWells, Inc. stereotactic systems illustrate the use of stereotactic frames and recording probes.
The capability to advance an electrode in fine steps, on the order of several tens of microns (micrometers) to several hundred microns presents certain technical problems. Mechanical motions of the electrode or the advancing device can disturb the highly sensitive electrical recording measurements of electrical brain activity. For similar reasons, it may be advantageous to electrically decouple moving device from the electrode. Hydraulic microdrives have been used to provide fine verniated movements. The hydraulic microdrives comprise a flexible hydraulic tubing that advances an incompressible fluid within the tubing to drive a piston which is coupled to the electrode near the stereotactic frame. By reference, the electrode microdrive of the TrentWells, Inc. company (Los Angeles, Calif.) is an example of a hydraulically advanced microdrive for stereotactic probes.
Difficulties with hydraulic microdrives include fluid leaks and problems with sterilization. For example, steam autoclave sterilization disrupts the hydraulic fluids that are contained in the enclosed, flexible tubing. Furthermore, the ability to monitor the position of the electrode at the position of the probe carrier on the stereotactic frame has been difficult. By reference, the hydraulic probe microdrive of the TrentWells, Inc. company does not provide detection means at the probe end near the stereotactic frame end of the hydraulic tubing. Rather, this microdrive only provides deflection means at the side near the hydraulic piston, which is remote from the stereotactic frame.
It is important for a surgeon to know the actual position of the probe at the stereotactic frame for quantitative evaluation of the position of the probe. However, mechanical screw type, rack-and-pinion, or millimeter slide type probe carriers on the stereotactic frame prove relatively ineffective in achieving fine distance verniations (e.g. on the order of tens of microns) without creating electrical disturbance of the brain recordings.
Accordingly, an effective technique and system for stereotactic probe advancement, especially when fine advanced movements are required and electrical recording is required, is desirable for purposes of stereotactic probe placement. Particularly in the surgical setting, a need exists for a microdrive for probes which does not rely on fluid coupling and which can be readily cleaned and sterilized.
The present invention is directed to a mechanical microdrive system and method for smooth and reliable advancement of a probe with respect to a probe carrier. The present invention is different from any of the systems discussed in the Background section. Advantages of the present system and method reside in their simplicity, mechanical stability, ability to be sterilized and cleaned for surgical use, ruggedness and reliability, and clinical effectiveness.
In one embodiment, the mechanical microdrive includes flexible tubing that contains a flexible but longitudinally rigid push cable (push rod). The tubing is connected on its distal end to a stereotacic carrier attached to a stereotactic frame. The flexible push rod is attached independently to a microelectrode holder that advances the microelectrode stereotactically into the patient""s body. On the proximal end, the flexible tubing is attached to a platform, and the flexible push rod is advanced within the tubing by an advancing mechanism. The advancing mechanism can have very fine longitudinal position gradations and have readout and display of its position. It is driven either manually or by a motor. At the stereotactic frame, the relative position of the probe is measured by a detecting system to give a position of the advancement of the probe into the patient""s body. Electrical signals from the driving mechanism and the probe position mechanism can be sent to a computer or other display to control the process.
One embodiment of the mechanical flexible advancement device utilizes a longitudinal advancement of the push rod within the device as provided by a rotatable internal drive rod which enables a screw advancement at the proximal end by the stereotactic device.
The present technique avoids many of the difficulties associated with a hydraulic microdrive. For example, since a hydraulic transmission fluid is not used within the system, difficulties of autoclaving and unwanted leaks are avoided. In addition, a system conducted according to the present invention may be cleaned and sterilized by using autoclave and other means, thus simplifying the surgical preparation. Such a system has further advances of simplicity and robustness. It does not need to be filled with a hydraulic fluid and does not have problems associated with bubble formation within the hydraulic tube, as does the hydraulic microdrive described in the Background section.
These features and advantages, as well as others of the present method and system, will become apparent in the detailed description that follows.